The long-term aim of the proposed project is to define the structure-function relationships of apoB and its role in atherogenesis by studying naturally-occurring human variants of apoB detected by immunochemical and sizing procedures. Plasmas of hypo- and non-familial hypercholesterolemic individuals identified by screening in "walk-in" clinics and in the Lipid clinic, and of unselected patients undergoing coronary angiography will be tested. Competitive radioimmunoassays and 3-6% polyacrylamide gradient SDS gel electrophoresis and Western blotting using a panel of monoclonal antiapob antibodies directed against the major regions of apoB-100 will be used to identify size- or immunogenetic variants of aPoB. To ascertain the patterns of inheritance of any variants, families of affected individuals also will be similarly tested. Special structural and functionality studies will be performed in probands, selected members of their kindreds, and appropriate control subjects. The special study protocols are meant to characterize the physicochemical and immunochemical properties of lipoproteins and the interactions of LDLs containing normal end variant apoBs with fibroblast LDL receptor, mouse macrophage scavenger receptors, and heparin. The responses of subjects to a fat meal containing vitamin A and to 6 days of a minimal fat diet will be assessed in order to judge the ability of intestine and liver to produce lipoproteins and to attempt {o deduce the tissue source of the variant apoB. Kinetic studies using 15N-glycine and GC-mass spectrometry will be carried out to assess whether altered levels of variants ere due to atherogenesis or catabolism of apoB. Finally, molecular studies on the protein and gene level will be performed to characterize molecular defects. This comprehensive study should provide information on the structure-function relationship of apoB and relate features of apoB structure to the atherogenecity (or lack thereof) of apoB-containing lipoproteins.